Semiconductor wafer and processing method for same

ABSTRACT

A semiconductor wafer which is generally circular, and which has on its face an annular surplus region present in an outer peripheral edge portion of the face, and a circular device region surrounded by the surplus region, the device region having many semiconductor devices disposed therein. A circular concavity is formed in the back of the semiconductor wafer in correspondence with the device region, and the device region is relatively thin, while the surplus region is relatively thick.

FIELD OF THE INVENTION

This invention relates to a semiconductor wafer which is generallycircular, and which has on the face thereof a surplus region present inan outer peripheral edge portion of the face, and a circular deviceregion surrounded by the surplus region, the device region having manysemiconductor devices disposed therein; and a processing method for sucha semiconductor wafer.

DESCRIPTION OF THE PRIOR ART

As is well known among people skilled in the art, it is common practicein the manufacture of a semiconductor device to dispose manysemiconductor devices on the face of a generally circular semiconductorwafer, then grind the back of the semiconductor device to decrease thethickness of the semiconductor device to a required value, then, ifnecessary, conduct a required test, such as a probe test, on each of thesemiconductor devices, and then dice the semiconductor wafer to separatethe semiconductor devices individually.

In recent times, it is often desired to grind the back of thesemiconductor wafer, thereby rendering the thickness of thesemiconductor wafer markedly small, for example, 50 μm or smaller, forthe purpose of downsizing and weight reduction of the semiconductordevice. However, if the thickness of the semiconductor wafer is renderedvery small, the rigidity of the semiconductor wafer is markedly low.Thus, the semiconductor wafer is difficult to handle, and the risk ofdamage to the semiconductor wafer is also incurred.

SUMMARY OF THE INVENTION

It is a first object of the present invention, therefore, to provide anovel and improved semiconductor wafer which can avoid difficulty inhandling the semiconductor wafer and can minimize the risk of damagingthe semiconductor wafer, while fulfilling the requirements fordownsizing and weight reduction of semiconductor devices.

It is a second object of the present invention to provide a novel andimproved processing method for a semiconductor wafer which is designedto form the above novel and improved semiconductor wafer.

The inventor conducted in-depth studies, and has noticed that on theface of a semiconductor wafer, there are a surplus region present in anouter peripheral edge portion of the face, and a circular device regionsurrounded by the surplus region, and many semiconductor devices aredisposed in the device region. Based on these facts, the inventor hasfound that the above first and second objects can be attained by forminga circular concavity in the back of the semiconductor wafer incorrespondence with the device region to decrease the thickness of thedevice region of the semiconductor wafer to a required value, but renderthe thickness of the surplus region of the semiconductor waferrelatively large, instead of grinding the entire back of thesemiconductor wafer to decrease the entire thickness of thesemiconductor wafer.

According to the present invention, there is provided, as asemiconductor wafer for attaining the above first object, asemiconductor wafer which is generally circular, and which has on theface thereof an annular surplus region present in an outer peripheraledge portion of the face, and a circular device region surrounded by thesurplus region, the device region having many semiconductor devicesdisposed therein, and

wherein a circular concavity is formed in the back of the semiconductorwafer in correspondence with the device region, and the device region isrelatively thin, while the surplus region is relatively thick.

The width of the surplus region is preferably 2.0 to 3.0 mm. Preferably,the thickness of the surplus region is 250 μm or more, particularly 300to 700 μm, while the thickness of the device region is 100 μm or less,particularly 30 to 50 μm.

According to the present invention, moreover, there is provided, as aprocessing method for a semiconductor wafer for attaining the abovesecond object, a processing method for a semiconductor wafer which isgenerally circular, and which has on the face thereof an annular surplusregion present in an outer peripheral edge portion of the face, and acircular device region surrounded by the surplus region, the deviceregion having many semiconductor devices disposed therein,

the processing method comprising forming a circular concavity in theback of the semiconductor wafer in correspondence with the device regionto decrease the thickness of the device region.

Preferably, the circular concavity is formed by grinding the back of thesemiconductor wafer. Particularly, it is preferred to form the circularconcavity by grinding the back of the semiconductor wafer by means of agrinding tool having a plurality of arcuate grinding members arranged ina generally toroidal form, or a toroidal grinding member, the grindingmembers or the grinding member having an outer diameter somewhat largerthan the radius of the circular concavity. When grinding the back of thesemiconductor wafer by means of the grinding tool, it is preferred toposition the grinding tool relative to the semiconductor wafer such thatthe outer peripheral edge of the grinding members or the grinding memberis inscribed in the outer peripheral edge of the device region, and thelower surface of the grinding members or the grinding member straddlesthe center of the semiconductor wafer, to rotate the semiconductor waferabout the central axis of the semiconductor wafer, to rotate thegrinding tool about the central axis of the grinding members or thegrinding member, and to move the grinding tool toward the semiconductorwafer in the direction of the central axis. After the circular concavityis formed, the semiconductor wafer is cut along the outer peripheraledge of the device region to remove the surplus region, and then thedevice region is diced, whereby the semiconductor devices can beseparated individually. Alternatively, a circular auxiliary membercorresponding to the circular concavity is accommodated in the circularconcavity, and then the surplus region is diced along with the deviceregion, whereby the semiconductor devices can be separated individually.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a semiconductor wafer before beingprocessed according to the present invention.

FIG. 2 is a schematic sectional view showing a manner in which the backof the wafer in FIG. 1 is ground to form a circular concavity.

FIG. 3 is a schematic plan view showing the relationship between thewafer and grinding members of a grinding tool when the back of the wafer2 is ground in the manner shown in FIG. 2.

FIG. 4 is a perspective view showing a preferred embodiment of the waferof the present invention having the circular concavity formed in theback of the wafer.

FIG. 5 is a perspective view for illustrating a mode of dicing the waferof FIG. 4.

FIG. 6 is a perspective view for illustrating the way of using anauxiliary member for use in a different mode of dicing the wafer of FIG.4.

FIG. 7 is a perspective view for illustrating the above different modeof dicing the wafer of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical example of a semiconductor wafer 2 well known perse before being processed which is subjected to processing (to bedescribed later) to configure a semiconductor wafer according to thepresent invention. The illustrated wafer 2 is circular as a whole, andhas an orientation notch 4 formed in a circumferential edge portionthereof. The thickness of the wafer 2 is uniform throughout, and ispreferably 250 μm or more, especially 300 to 700 μm. On the face 6 ofthe wafer 2 there are an annular surplus region 6 a present in an outerperipheral edge portion of the face 6, and a circular device region 6 bsurrounded with the surplus region 6 a. The notch 4 is formed in theannular surplus region 6 a. The circular device region 6 b has manyrectangular regions 10 partitioned by streets 8 arranged in a latticepattern, and a semiconductor device is disposed in each of therectangular regions 10.

In the present invention, a circular concavity 12 (FIG. 4) is formed inthe back of the wafer 2 in correspondence with the circular deviceregion 6 b. With reference to FIG. 2 showing a preferred method forforming the circular concavity 12, a protective tape 14, which may be asuitable plastic film, is stuck to the face of the wafer 2. Such a wafer2 is placed on a substantially horizontal upper surface of a chuck table18, with the wafer 2 being turned upside down, namely, the back 16 ofthe wafer 2 being exposed upward. The chuck table 18 is mounted to berotatable about a central axis 20 extending vertically, and is rotatedby a rotational drive source (not shown). The chuck table 18 is formedof a porous material, or a suction hole or-groove (not shown) is formedin the surface of the chuck table 18, so that the wafer 2 is attractedunder vacuum onto the chuck table 18 by connecting the chuck table 18 toa suitable suction source (not shown).

A grinding tool 22 is caused to act on the back 16 of the wafer 2attracted onto the chuck table 18 to form the circular concavity 12 inthe back 16 of the wafer 2. The grinding tool 22 is mounted to berotatable about a central axis 24 extending vertically, and is rotatedat a high speed by a rotational drive source (not shown). Theillustrated grinding tool 22 includes a support member 26 having acylindrical lower end portion, and a plurality of grinding members 28fixed to the lower end surface of the support member 26. The grindingmembers 28, which can be formed from diamond grains bonded together by asuitable bonding material, are each arcuate, and arranged with spacingin the circumferential direction to assume a toroidal form as a whole.Instead of the plural grinding members 28 each of an arcuate shape, asingle toroidal grinding member (not shown) can be fixed to the lowersurface of the support member 26.

In a preferred processing method according to the present invention,there is used the grinding tool 22 in which the outer diameter D2 of thegrinding members 28 is somewhat larger than the radius D1 of thecircular concavity 12 to be formed. As shown in FIGS. 2 and 3, thegrinding tool 22 is positioned relative to the wafer 2 such that theouter peripheral edge of the grinding members 28 is inscribed in theouter peripheral edge of the device region 6 b (accordingly, the innerperipheral edge of the circular concavity 12 to be formed), and thegrinding member 28 straddles the central axis 20 of the wafer 2. In thisstate, the chuck table 18 is rotated about the central axis 20, thegrinding tool 22 is rotated about the central axis 24, and the grindingtool 22 is gradually moved, namely, lowered toward the wafer 2. In thismanner, the back 16 of the wafer 2 is ground in correspondence with thedevice region 6 b to form the circular concavity 12. The thickness ofthe wafer 2 in the device region 6 b after formation of the circularconcavity 12 is preferably 100 pm or less, especially 30 to 50 μm. FIG.4 shows the wafer 2 having the circular concavity 12 formed in the back16, with the wafer being turned upside down. In the wafer 2 shown inFIG. 4, the device region 6 b is markedly thin, whereas the annularsurplus region 6 a surrounding the device region 6 b is relativelythick, so that the wafer 2 as a whole has adequate rigidity.

If desired, it is possible to form the circular concavity 12 in the back16 of the wafer 2 by plasma etching, sputter etching, orchemical-mechanical-polishing, instead of forming the circular concavity12 in the back 16 of the wafer 2 by grinding.

The wafer 2 having the circular concavity 12 formed therein can, ifdesired, be further subjected to suitable processing. For example, athin film comprising a metal, such as gold, silver or titanium, can beformed on the back 16 of the wafer 2 by a sputtering method well knownper se. Moreover, the protective tape 14 stuck to the face 6 of thewafer 2 can be peeled from the wafer 2 to expose the face 6, and a probetest well known per se can be conducted on the semiconductor devicedisposed in each of the rectangular regions 10. In applying requiredprocessing to the wafer 2, an operation, such as transport of the wafer2, can be performed sufficiently easily, and the risk of damage to thewafer 2 can be fully avoided, because the rigidity of the wafer 2 isrelatively great owing the presence of the annular surplus region 6 ahaving a relatively large thickness.

After the required processing is performed for the wafer 2, the wafer 2is diced, namely, the wafer 2 is cut along the streets 8 arranged in alattice pattern in the device region 6 b on the face 6, to separate therectangular regions 10 individually.

In one mode of dicing the wafer 2, the wafer 2 is first cut along theouter peripheral edge of the device region 6 b to remove the annularsurplus region 6 a. Such cutting of the wafer 2 can be advantageouslyperformed, for example, by irradiating the wafer 2 with a pulsed laserbeam along the outer peripheral edge of the device region 6 b. Then, asshown in FIG. 5, the wafer 2 is mounted on a frame 32 via a mountingtape 30. In further detail, the frame 32, which can be formed from aplate of a metal, such as aluminum, or a suitable synthetic resin, has amounting opening 34 in its middle portion. The wafer 2 deprived of theannular surplus region 6 a is positioned in the mounting opening 34, andthe mounting tape 30 is stuck to the back of the frame 32 and the back16 of the wafer 2, whereby the wafer 2 is mounted on the frame 32. Thewafer 2 mounted on the frame 32 can be diced, namely, cut along thestreets 8 in the device region 6 b, by a well known cutting machinecalled a dicer. Preferred examples of the dicer are those having anultrathin ring-shaped blade containing diamond grains as a cuttingmeans, or those having a pulsed laser beam application means as acutting means.

Another mode of dicing the wafer 2 is to mount an auxiliary member 36 inthe middle portion of the mounting opening 34 of the frame 32 via themounting tape 30, before mounting the wafer 2 on the frame 32, as shownin FIG. 6. In other words, the auxiliary member 36 is positioned in themounting opening 34 of the frame 32, and the mounting tape 30 is stuckto the back of the frame 32 and the back of the auxiliary member 36. Theauxiliary member 36, which can be formed from a suitable synthetic resinor a suitable metal, is a disk having a shape corresponding to thecircular concavity 12 formed in the back 16 of the wafer 2, namely, acircular plane shape corresponding to the circular concavity 12, and athickness corresponding to the depth of the circular concavity 12. Then,as shown in FIG. 7, the wafer 2 is positioned such that the auxiliarymember 36 is accommodated in the circular concavity 12 formed in theback 16, whereafter the back of the annular surplus region 6 a of thewafer 2 is stuck to the mounting tape 30. In this manner, the wafer 2 ismounted in the mounting opening 34 of the frame 32. The wafer 2 and theauxiliary member 36, which have been mounted in the frame 32, complementeach other to constitute a disk having a uniform thickness as a whole.Then, the wafer 2 is diced, namely, cut along the streets 8 in thedevice region 6 b, by a well known cutting machine.

While the preferred embodiments of the present invention have beendescribed in detail by reference to the accompanying drawings, it is tobe understood that the invention is not limited to such embodiments, butvarious changes and modifications may be made without departing from thescope of the invention.

1-4. (canceled)
 5. A processing method for a semiconductor wafer whichis generally circular, and which has on a face thereof an annularsurplus region present in an outer peripheral edge portion of the face,and a circular device region surrounded by the surplus region, thedevice region having many semiconductor devices disposed therein, theprocessing method comprising forming a circular concavity in a back ofthe semiconductor wafer in correspondence with the device region todecrease a thickness of the device region.
 6. The processing methodaccording to claim 5, further comprising grinding the back of thesemiconductor wafer to form the circular concavity.
 7. The processingmethod according to claim 6, further comprising: forming the circularconcavity by grinding the back of the semiconductor wafer by means of agrinding tool having a plurality of arcuate grinding members arranged ina generally toroidal form, or a toroidal grinding member, the grindingmembers or the grinding member having an outer diameter somewhat largerthan a radius of the circular concavity; and when grinding the back ofthe semiconductor wafer by means of the grinding tool, positioning thegrinding tool relative to the semiconductor wafer such that an outerperipheral edge of the grinding members or the grinding member isinscribed in an outer peripheral edge of the device region, and a lowersurface of the grinding members or the grinding member straddles acenter of the semiconductor wafer, rotating the semiconductor waferabout a central axis of the semiconductor wafer, rotating the grindingtool about a central axis of the grinding members or the grindingmember, and moving the grinding tool toward the semiconductor wafer in adirection of the central axis.
 8. The processing method according toclaim 5, further comprising: after forming the circular concavity,cutting the semiconductor wafer along an outer peripheral edge of thedevice region to remove the surplus region; and then dicing the deviceregion to separate the semiconductor devices individually.
 9. Theprocessing method according to claim 5, further comprising:accommodating a circular auxiliary member corresponding to the circularconcavity into the circular concavity; and then dicing the surplusregion along with the device region to separate the semiconductordevices individually.